Characterization of genes that suppress testicular germ cell tumor (TGCT) progression in mice will improve our understanding of primordial germ cell (PGC) development and provide new targets for the treatment of TGCTs in humans. The /4y mutation, which deletes Raly and Eif2s2 and causes the ectopic expression of agouti, decreases TGCT susceptibility in 129/Sv and 129.Chr19M mice. In contrast, preliminary studies suggest that the >Avy mutation, which maintains Raly and Eif2s2 and induces the ectopic expression of agouti from an IAP insertion, does not decrease TGCT frequency in 129.Chr19M mice. Together these results suggest that the deletion of Raly or Eif2s2 and not the ubiquitous expression of agouti decreases TGCT frequency in Ay mice. Both Raly and Eif2s2 have distinct functions in RNA biology, which plays a central role in PGC development and TGCT progression. Therefore, Raly and Eif2s2 are excellent candidate TGCT suppressor genes. This proposal will test 1) the contributions of the Raly and Eif2s2 deletions on the decreased TGCT frequency in 129.Chr19M, Ay/+ mice using BAG transgene complementation tests and conditional knockout mice, and 2) the TGCT frequency and expression levels of Raly and Eif2s2 in 129./W+ and 129.Chr19M, Avy/+ mice.